Sati is considered as first wife of Lord shiva. Sati was born as human being, and as daughter of King Daksha Prajapati and queen Prasuti. From childhood Sati develops love and Bhakti over lord shiva.

And starts praying to get Lord shiva as her husband..

Daksha does not approve of this and wants to marry of his daughter to Rich Kings... Sati then peforms severe penance and lord shiva bless her and promise to marry her...

Daksha got his daughter married to Lord shiva against his wishes..Once Daksha organized a grand Yagna to which all the gods were invited, with the exception of Sati and Shiva. Sati wanted to visit and tried to convince shiva that Daksha did not invite them, as they are family and she needs no invitation to visit her parents, however unwillingly shiva sent only Sati to the Yagna.

Here at the Yagna, Daksha did not welcome his daughter and start insulting Lord shiva, Sati could not bare Shiva Ninde (Abuse to Shiva) and regrets for not listening to shiva's words to not come here.

She immediately jumps into the Fire prepared for the Yagna, as a punishment to not followingshiva's words and was reason of shiva Ninde...

This news reaches to Lord shiva, and Shiva fumes and creates Veerabhadra, an Amsha(Part) of shiva itself.. Veerbhadra reaches yagna place, and kills everybody destroys Yagna, and carriesSati's body to Lord Shiva.

Lord shiva struck with grief, carries Sati's bodies on his shoulders and performs Shiva Tandava, to this force of Shiva's dance, Sati's body is ripped and falls on 51 places.. Later this 51 places turned to Piligrimage center forming Shaki Peetas.Later Lord Vishnu Pacifies Lord shiva and says Sati will be again born as Parvati, who will again Marry Lord shiva.